The answer is: 40 years

1 Ki 2:11

King David, one of the most celebrated figures in biblical history, reigned for 40 years, marking an influential era in Israel's story. His reign can be broken into two main parts: 7 years spent as king of Judah in Hebron and 33 years as king over all Israel in Jerusalem, the capital he established. This 40-year window is often likened to the 40 years that the Israelites wandered in the desert, signifying both trial and fulfillment.

There are interesting connections in literature as well: The New Testament alludes to David's legacy frequently, emphasizing his importance. For instance, Jesus is often referred to as the "Son of David," instantly linking his mission to the nearly millennia-old reign of the shepherd king.

David's life wasn't just marked by royal decisions; it's also a reminder of the complexity of leadership. He was an incredibly talented musician, a warrior, and a poise instigator of political peace, but he also faced serious personal fails, such as his adultery with Bathsheba that led to deeply tragic events in his family. This dichotomy has drawn debates regarding mistake-filled human life juxtaposed against belief in divine purposes.

Engaging with his story highlights essential themes like the nature of repentance, the tyranny of guilt, and the possibility of new beginnings. Remember, David is dynamic, embodying the ups and downs of human experience and the weaving of divinity into history!